U.S. patent application of Ser. No. 516,687 filed on July 25, 1983 now U.S. Pat. No. 4,549,542 by the same applicant discloses a multiple-effect respirator comprising a driving motor, a supplying air fan, an exhausting air fan, two ventilating air fans and a mask wherein all the fans are mounted on a helmet and commonly driven by the single motor so that the driving force of the motor is only partially distributed to supplying air fan and exhausting air fan for circulating the air for wearer's breathing as partial driving force of the motor is shared by the two ventilating fans directing air into wearer's helmet to thereby greatly reduce the forced circulation effect within the mask.
The present inventor has found this defect and invented the present respiratory mask.